TALKS chief Richard Haass is to decide in the next few days if he will return to Northern Ireland to attempt to push a deal between Stormont's parties over the line.

But he and his vice-chair Meghan O'Sullivan have made clear they cannot remain in the province in the New Year because of other commitments, believed to include a trip to Australia.

"We would like to think there is reason to return," Dr Haass told reporters after a marathon talks session broke up without agreement at 4am on Christmas Eve.

He will first, however, make an assessment of the five main parties responses to questions he is to send to them in the next few days.

They are due to be emailed to the DUP, Sinn Fein, UUP, SDLP and Alliance negotiators who are expected to reply by Monday.

There is growing speculation the negotiations will continue into 2014 – even though agreement on flags has been shelved.

Secretary of State Theresa Villiers said she hoped work could continue after Christmas and praised the commitment in trying to reach agreement.

"The UK Government will continue to support the efforts made by the Northern Ireland parties as they seek a way forward. I also welcome the enthusiastic support offered by the Irish Government for this process," she said.

"The prize of an agreement is more important than any deadline," said one source after more than seven hours of plenary sessions, bilateral and trilateral meetings between the parties stretching from just before 9pm to the wee small hours of 4am.

Dr Haass and Dr O'Sullivan were booked on a flight out of Dublin at 10am.

He said "significant differences and divisions" remained on all three issues he was asked to help find a solution for.

"The work done on flags is quite disappointing by any measure," he added. "But the other two areas have been, I believe, quite impressive and I believe it would be a real shame not to be able to turn that work into a reality.

"Let me be clear about this – we don't have an agreement (but) in no way have we given up the possibility of reaching an agreement before the end of the year.

"We are not going to be able to put it underneath anyone's Christmas tree, but we still have a week and if there is reason to return – I think we will have the answer to that question when we get the responses to a new draft that we will produce over the next few days – then both of us are willing to come back here, fly back here and give it one last push."

Answering questions in the Stormont Hotel, he went on: "I am not in the business of doing post- mortems here, because the patient is still alive."

The DUP's Jeffrey Donaldson admitted there was disappointment but the parties "have to be realistic".

Sinn Fein's Gerry Kelly said his party's executive mandated negotiators to achieve a deal and it was disappointing "we weren't able to do that".

UUP leader Mike Nesbitt said: "We didn't get there tonight but I think we did get real in terms of a better understanding of where everybody's bottom line is.

"So I remain optimistic."

Former SDLP minister Alex Attwood said: "We said to Richard Haass and Meghan O'Sullivan 'A safe home over the Atlantic and we will see you next weekend back in Belfast', because whilst we haven't got a Christmas Eve deal we can still achieve a New Year's Eve deal, and that is the purpose of the next week."

But Alliance's Naomi Long warned while the talks were not dead. they were on "life support".